gas resistant (proof?) adhesive

I am asking a question with this suggestion. I do not know enough about the heat shrink tube to say it could work. But have had a thought of cutting a ring of the correct tube and use it like the ring you had to cut off on the stock setup. Once in the correct location heat it and it may seal it to the slide? 

That's a thought. I've never used it but they do make Viton heat shrink. I wonder if it might work better as an underlayment though, along the lines of the JB weld idea but doesn't need a lathe (that I don't have anyway).

If you try the heat shrink go with the Marine type, it has a glue/sealant in the inside. That may be a good idea.